Crucible furnace



Oct. 10, 1939. I. HALL 2,175,462

CRUC IBLE FURNACE Filed June 13, 1939 4 Sheets-Sheet l PIC-3.]. m ll Z8 Z Z5 Z6 30 I J O 0 7 Isaiah 5% Oct. 10, 1939. l, HALL 2,175,462

CRUC IBLE FURNACE Filed June 13, 1939 4 SheetsSheet 2 A f/a 11 wel s Oct. 10, 1939. 1. HALL 2,175,462

CRUCIBLE FURNACE Filed June 13, 1939 4 Sheets-Sheet 3 mumriimnmesl g Isaiah 7 a Patented Oct. 10, 1939 UNITED STATES PATENT OFFICE Application June 13, 1939, Serial No. 278,947 In Great Britain February 18, 1938 14 Claims.

This invention relates to tilting furnaces for melting and refining metals and of the kind in which a crucible or pot of metal, graphite, clay or other refractory material, is mounted vertically within a furnace body and spaced from the walls thereof by a heating chamber in or through which are circulated the heating gases or products of combustion, the furnace body being tiltable to permit pouring of the metal from the crucible without removing the latter from the furnace body.

The invention is primarily concerned with gas or oil fired furnaces of this kind.

Referring to the drawings- Figure 1 is an end elevation of one construction according to this invention.

Figure 2 is a plan view of same.

Figure 3 shows the same in front elevation.

Figure 4 is a view similar to Figure 1 but with the furnace bodyin section.

Figure 5 is an end elevation of a modification.

Figure 6 shows the same in front elevation.

Figure 7 is a view similar to Figure 5 but to a larger scale and on a section taken through the furnace.

Figure 8 is an elevation of a detail.

Figure 9 is a section through part of a slight modification.

In Figures 1 to 4 is illustrated a furnace including a pair of spaced vertical pedestals 6 each of which has at its'upper end a bearing 1 and between these pedestals is mounted the body of the furnace including a metal casing 9 to which is secured at diametrically opposite positions a pair of trunnions 8 engaging in the bearings l on the furnace is a crucible or pot II supported on a refractory stool [2.

The crucible, which may be formed from plumbago or other refractory material, is of external diameter less than the internal diameter of the lined body of the furnace so that an annular heating chamber I3 is provided around the crucible, this chamber being of greater volume at the lower part of the furnace due to the reduction in the diameter of the crucible and to a reduction in the thickness of the refractory lining Ifl.

When the refractory lining i is costructed of plastic refractory material a convenient method of shaping this material and forming the heating chamber i3 is to use a sheet metal circular template upon which is positioned a guided tool carrier with a cutting tool for shaping the refractory material, this tool carrier being operated from the top of the template.

Communicating with the lower part of the heating chamber is a combustion chamber l4 formed in part by a lateral opening through the lower part of the lining It] at the back of the furnace and in part by a refractory sleeve l5 within a metal sleeve l6 secured to the exterior 10 of the casing 9.

At the front of the furnacebody there is an inspection opening closed by an inspection door ll, whilst in the base of the furnace there are a pair of hinged drop-down blocks I8 normally retained in the closed position by a releasable catch [9 mounted slidably upon the channel below the base of the furnace.

In the event of fracture of the crucible ll any 'metal leaking into the body of the furnace can 20 be removed by releasing the catch [9 and allowing the blocks 18 to drop down to the position indicated in dotted lines in Figure l, the metal being collected in a suitable pit below the base of the furnace.

' Secured to the top of the casing 53 at the back of the furnace is an exhaust branch 2| lined with refractory material and communicating with an exhaust passage 22 formed through the lining I0 and in this branch 2| is mounted a pivoted 3O butterfly valve or baffle 23 for control of the passage of exhaust gases from the heating chamher.

To the top of the casing 9 there is fixed a flange 24 to which is bolted a separate domed top or charging head 25 having a flange seating'on and bolted to the flange 24 on the casing.

Readily releasable bolts, pins or studs, such for example as bolts provided with wing nuts, may be used for securing the head in position and a sealing washer of asbestos or other material may be provided between the flanges on the furnace body and the domed top 25 so as to seal the joint and enable separation of the domed top from the body of the furnace when desired.

Lifting bolts 26 are provided on the domed top which can be lifted or hoisted clear of the body of the furnace to enable replacement of the crucible for cleaning or re-lining of the furnace.

The top 25, which is of annular form in plan, is fabricated from sheet metal parts welded together and is hollow with a continuous passage 27 extending therethrough, this passage connecting a pair of hollow bosses 28 with which communicate air intake and outlet branches 29 and 30 respectively.

The intake branch 29 communicates with an air supply pipe 3! provided with a suitable control valve, whilst the outlet branch 30 extends down to the burner 32 arranged adjacent the combustion chamber as shown in Figures 1 and 4.

The burner is supported on an arm 33 and is supplied with oil, gas or other fuel through the pipe having a control valve J5.

Control of the supply of air to the burner is effected by a slide valve 36, whilst fine adjustments of the flow of fuel to the burner are made by means of a valve operated by the handle 37.

The furnace is adapted for tilting movement around the axis joining the trunnions 8 and the tilting mechanism includes worm and worm wheel or similar gearing mounted in a casing 38 on one of the pedestals 6, such gearing being operated by the hand wheel 39 and rotating the appropriate trunnion 8 to tilt the furnace as will be referred to later herein.

The furnace may be otherwise constructed to be tilted by hand or mechanically by means including a motor or motors.

To enable disconnection of the intake and outlet air branches during tilting of the furnace, a sealed detachable air connection is provided in each of these branches, each such connection including a pair of collars 40 and 4| secured one to each of two separate parts of the air branch, these collars having corresponding coned or partspherical seatings as shown in Figure 4.

The construction of the furnace is such that the slightly unbalanced weight of the combustion chamber, exhaust branch and intake and outlet air branches holds the furnace in the position shown in Figure 4 in which the detachable connections are seated firmly together to provide a readily detachable airtight joint in each air branch.

The top of the crucible is extended through the domed top of the furnace and is closed by a removable lid 42, whilst the annular heating chamber is closed or blocked-off by a ring 43 of firebrick or other refractory material filling the gap between the interior of the annular charging head and the exterior of the top of the crucible. The ring 43 may be built up from separate bricks suitably united together,

In operation the burner 32 fires into the combustion chamber l4 and the hot gases or products of combustion circulate around the crucible and in the heating chamber l3 to exhaust through the branch 2| from the top of the heating chamber.

The air for combustion is: pre-heated by passage through the preheater passage 21 in the domed top of the furnace and a substantial degree of preheating can be obtained in this manner, this increasing the effective furnace temperature in all types of furnace and being particularly advantageous with oil heated furnaces in facilitating or increasing vapourisation of the oil prior to combustion.

After melting or refining of the contents of the crucible the lid 42 is removed, the supply to the burner is cut off and the furnace is tilted by operation of the hand wheel 39 until the molten metal is poured from the top of the crucible into a suitable mould or receptacle.

Figures 1 to 4 illustrate the application of the invention to central axis tilting furnaces but in Figures 5 to 8 is shown the application of the invention to a true lip axis tilting furnace.

In the construction illustrated in Figures 6 to 8 the body of the furnace is constructed substantially as described with reference to Figures 1 to 4, namely, including outer casing 9, lined at ID to form the heating chamber l3, combustion chamber [4 and exhaust branch 2! all supported on trunnions 8 mounted in bearings I on a pair of vertical pedestals 6.

In this construction, however, the domed top or charging head 25 of the furnace is 01' cast instead of fabricated construction but as in the previously described construction this head is hollow and has an internal prehcater passage 2'! connecting a pair of hollow bosses with which communicate intake and outlet air branches 29 and 30 connected respectively to the air supply pipe 3| and the burner 32, each through a detachable air connection as described with reference to Figures 1 to 4.

The open top of the crucible H is disposed at or about the level at which the head 25 seats upon the main body of the furnace and from the top lip of the crucible a sleeve 44 extends upwardly through the top 25 to a height slightly above that of the head of the furnace to facilitate charging of the crucible.

This sleeve, which may be formed from plumbago or other refractory material may be sealed to the top of the crucible and a sealing ring or layer of any convenient material may be provided at the junction between the sleeve 44 and the top edge of the crucible.

The open top of the sleeve 44 is closed by a lid 42 lined with plumbago or other refractory material.

The annular heating chamber is closed or blocked-01f by an annular member 45 of refractory material carried by the head 25 and formed either as a ring of refractory material or built up from separate bricks suitably united together.

This member 45 fits closely within the head 25 and has at its upper end an upwardly projecting flange 46 resting upon the head 25 and at its lower end an inwardly projecting flange or thickened portion 41 extending to the exterior of the crucible at a plane below that of the top edge of the crucible and below the junction between the latter and the sleeve 44.

A pouring spout 48 extends through a V or other opening in the lip of the crucible and is carried through the furnace wall just below the head 25, being sealed to the crucible by a ganistered or other suitable joint. This spout, which may be formed from metal, plumbago or other refractory material, serves for the insertion of a pyrometer for the measurement of the internal temperature of the crucible.

The tiltin of the furnace about its lip axis is controlled by worm and skew tilting gear including a skew gear unit 49 operated by a hand wheel 59 and connected through universal joints 5|, connecting rod 52 and worm and worm wheel gearing in a casing 53 to a horizontal shaft 54 mounted in hearings on the stationary framework of the furnace.

On this shaft 54 there is fixed a pair of chain wheels 55 and on each wheel is fixed a chain 56, the free end of which is connected to a balance weight 51.

To the shaft 54 between the wheels 55 there is fixed a larger Wheel 58 to which is anchored one end of a further chain 59.

The chain 59 extends downwardly behind the furnace body and. around a channel-like sector secured below the base of the. furnace body, the

lower end of the chain being fixed to the lower. end of the sector 60.

An electric sparking plug 6| is mounted in the sleeve It to communicate with a short passage leading to the combustion chamber l4 so that the burner can be fired electrically,

The main air supply pipe 31 leading to the air inlet branch 29 of the preheater passes through a control box 52 containing a valve for interrupting the supply of air to the preheater and this control box also contains a further valve for controlling the oil or gas supply to the pipe 63 leading to the burner 32.

The two valves are adapted to be controlled by a plunger 64 projecting from the top of the box for engagement with an abutment 65 on the base of the furnace. A coil spring 66 located beneath the head of the plunger 64 maintains the plunger in engagement with the abutment 65 and is adapted to move the plunger upwardly when the furnace is tilted.

The burner 32 is carried. at the upper end of a support 61 and as will be seen from Figure 8 the burner is carried on a bracket 68 adjustably mounted on the collar 69 at the upper end of the support 61.

After slackening the clamping screws 10 the bracket t3 can be adjusted upon the flange 69 to permit correct alignment of the burner with the entrance to the combustion chamber I l, after which the burner can be locked in the correct position by tightening the screw Hi.v

The operation of the furnace is as follows:

When in the normal position as shown in Figure '7 the crucible can be charged by removing the lid 42 and after turning on the air and fuel supplies the burner can be ignited electrically by means of the sparking plug GI and the products of combustion circulate in the heating chamber l3 to heat the furnace. a

In this position of the furnace the abutment 65 depresses the plunger 64 to the position shown in Figure '7 and this plunger opens the two valves to permit supply of fuel to the burner through the pipe 63 and supply of air to the'preheater through the air supply pipe 3| and the inlet branch 29.

On completion of the melting or refining of the crucible charge the furnace is tilted by operation of the hand wheel 50 which rotates the shaft 54 through Worm and skew tilting gear and the wheel 58 is rotated to wind up the chain 59 and thus tilt the furnace about its lip axis so that the molten charge is poured into a suitable mould through the spout 48.

Tilting of the furnace moves the abutment 65 away from the end of the plunger 54 and the spring 65 forces the plunger upwardly to close the air and fuel valves and thus automatically cut off both the air supply to the preheater and the oil or gas supply to the burner.

It is thus impossible for the burner to be left on whilst the furnace is tilted and the interruption and completion of the supplies is effected automatically by the movement of the furnace.

The worm and skew tilting gear including the universal joints 51 is very flexible in that it enables the hand wheel to be mounted on the fixed structure at any convenient height without affecting the operation of the gear or requiring adjustment of the transmission mechanism.

Figure 9 shows a slight modification in which two separate rings H and 72 are provided for closing the top of the heating chamber in place of the single sleeve 45.

This construction allows greater heat to reach the preheating chamber and is particularly suitable when melting high temperature metals.

These rings, which may be formed from any convenient refractory material, may each be formed as a single complete ring or may be built up from separate units or bricks as desired or convenient.

The ring 12, which has at its upper edge a; flange 13 seating upon the top of the lining ID, fits closely within the lining and has a thickened lower edge which closes the top of the annular heating chamber at a plane below the junction between the crucible and the sleeve 44.

The ring H has an outwardly projecting flange 14 resting on the top of the domed head 25 and has an inwardly directed flange extending to the exterior of the sleeve 44.

In all the constructions above described the top of the heating chamber is closed at a plane below that of the top of the crucible and possibility of the products of combustion contaminating the contents of the crucible is entirely eliminated.

The construction is, however, quite simple to construct and maintain in efficient operation and further, the furnace is extremely adaptable in that it enables easy replacement of the crucible for use in melting or refining any one of a number of different metals or alloys.

The extension of the crucible through and beyond the domed top or charging head of the furnace further protects the contents of the crucible and facilitates charging thereof, whilst in the construction shown in Figures 1 to 4 or when a sealed joint is provided between the crucible and the sleeve 45, the metal or alloy being melted in the crucible can be completely enclosed during the melting or refining operation.

Further, the possibility of contamination of the molten metal or alloy during pouring is minimized by the fact that the metal is poured direct from the crucible, whilst the latter is retained in position in the furnace and it is unnecessary to remove or touch the crucible during normal pouring operations.

The detachable air connections in the inlet and outlet branches 29 and 3t) facilitate the tilting operation and entirely eliminate undesirable flexible joints or pipes and after the furnace has returned to its normal position the joint in each air branch is automatically completed by the collars 40 and ll seating together to form air-.

tight joints.

By use of the preheater it is possible to obtain a considerable degree of preheating of the air for combustion and with an oil fired furnace the oil is atomised by this preheated air without any carbon deposit due to incomplete combustion;

Further, the preheater passage 27 forms an air reservoir and the accumulation of air in this preheater together with the effect of the increase of temperature of the air when in the preheater accordingly increases the pressure of the air passing to the outlet branch 38. Accordingly the air pressure at the burner is increased and in this way it is possible to get higher furnace temperatures even with low pressure fans. Normally it is impossible to obtain such high temperatures without installing high pressure fans but by using the preheater according to the present invention the temperatures can be obtained with low pressure fans.

In addition to providing means for preheating the air for combustion as above described, means Pil may be provided for heating the oil or fuel pipe to enable preheating of the oil or fuel passing to the burner or burners.

The control valve in the exhaust can also be used to regulate the temperature and operation of the furnace by enabling regulation of the discharge of the products of combustion or hot gases from the heating chamber.

When the replacement of the crucible is necessary the entire head with the rings d3, El and 2 can be removed. and as stated above this operation may be facilitated by providing readily detachable or releasable clamping bolts for the head.

The furnace particularly described and illustrated is extremely simple to construct and operate and can be worked by oil or gas firing in a very economical manner and adjustments of the firing and control of the temperature to produce various treatments can readily be effected by operation of the various controls above described.

Further, whilst of much less expensive and complicated construction the furnace has the advantages of an electric furnace as far as are concerned ease of operation and melting or treatment of the metal or alloy without contamination.

Crucible furnaces of this kind are generally comparatively small and adapted to handle charges of from about 109 lbs. to 3 tons of copper alloys or the like or from about 109 lbs. to 1 ton of aluminum or like alloys.

What I claim then is:

l. A tilting furnace including a supporting structure, a furnace body tiltably mounted on said structure, a crucible mounted in said furnace body and spaced from the walls thereof by a heating chamber for the circuiation of the heating gases, a top on said furnace body and a preheater in said top for preheating the a r for the furnace, said preheater extending in said fur nace top around the top of the crucible.

2. A tilting furnace including a supporting structure, a furnace body, means for tilting said furnace body on said structure, a crucible mounted in said furnace body and spaced from the walls thereof by a heating chamber for the circulation of the heating gases, a top on said furnace body, the top of the crucible extending upwardly through said furnace top and a preheater in said top for preheating the air for the furnace, said preheater comprising an chamber extending in said furnace top around the top of the crucible.

3. A tilting furnace including a supporting structure, a furnace body, means for tilting said furnace body on said structure, a crucible mounted in said furnace body and spaced from the walls thereof by a heating chamber for the circulation of the heating gases, a top on said furnace body, the top of the crucible extending upwardly through said furnace top, said heating chamber being closed at a level below that'of the top of the crucible so that the heating chamber is entirely separated from the interior of the crucible,

an exhaust branch leading from said heating chamber at a level below that at which said chamber is closed and a preheater in said top for preheating the air for the furnace.

4. A tilting furnace including a supporting structure, a furnace body, means for tilting said furnace body'on said structure, a crucible mounted in said furnace body and spaced from the walls thereof by a heating chamber for the circulation of the heating gases, a top on said furnace body,

an extension of said crucible extending upwardly through said furnace top, said extension comprising an open-ended sleeve of refractory material, said heating chamber being closed at a level below that of the top of the crucible and an exhaust branch leading from said heating chamber at a level below that at which said chamber is closed.

5. A tilting furnace including a supporting structure, a furnace body, means for tilting said furnace body on said structure, a crucible mounted in said furnace body and spaced from the walls thereof by a heating chamber for the circulation of the heating gases, a top on said furnace body, an extension on the top of said crucible extending upwardly through said furnace top, said extension comprising an open-ended sleeve of refractory material and a preheater in said top for preheating the air for the furnace, said preheater extending in said furnace top around the top of the crucible.

6. A tilting furnace including a supporting structure, a furnace body, means for tilting said furnace body on said structure, a crucible mounted in said furnace body and spaced from the walls thereof by a heating chamber for the circulation g? of the heating gases, 2. top on said furnace body, an extension of said crucible extending upwardly through said furnace top, said extension comprising an open-ended sleeve of refractory material and a preheater in said top for preheating the air for the furnace, said preheater comprising an annular chamber extending in said furnace top around the top of the crucible.

'7. A tilting furnace including a supporting structure, a furnace body, means for tilting said furnace body on said structure, a crucible mounted in said furnace body and spaced from the walls thereof by a heating chamber for the circulation of the heating gases, a top on said furnace body, an extension on the top of said crucible extending upwardly through said furnace top, a sealed joint between said crucible and said extension, said heating chamber being closed at a level below that of the top of the crucible so that the heating chamber is entirely separated from the interior of the crucible, an exhaust branch leading from said heating chamber at a level below that at which said chamber is closed and a preheater in said top for preheating the air for the furnace, said preheater comprising an annular chamber extending in said furnace top around the top of the crucible.

8. A tilting furnace including a supporting structure, a furnace body, means for tilting said furnace body on said structure, a crucible mounted in said furnace body and spaced from the Walls thereof by a heating chamber for the circulation of the heating gases, a top on said furnace body, said top comprising a detachable annular member of hollow section with a preheater passage eX- tending therethrough, means for conducting to and from said preheater furnace air for use in the furnace, said preheater passage extending in said furnace top around the top of the crucible.

9. A tilting furnace including a supporting structure, a furnace body, means for tilting said furnace body on said structure, a crucible mounted in said furnace body and spaced from the walls thereof by a heating chamber for the circulation of the heating gases, a top on said furnace body, said top comprising a detachable annular member of hollow section with a preheater passage extending therethrough, means for conducting to and from said preheater furnace air for use in the furnace, air inlet and outlet branches communicating with said passage, a detachable sealed connection in each of said branches, an annular member of refractory material between the top of the furnace body and the exterior of the crucible, said heating chamber being closed at a level below that of the top of the crucible so that the heating chamber is entirely separated from the interior of the crucible and an exhaust branch leading from said heating chamber at a level below that at which said chamber is closed.

10. A lip-axis tilting furnace including a supporting structure, a furnace body, means for tilting said furnace body on said structure, a crucible mounted in said furnace body and spaced from the walls thereof by a heating chamber for the circulation of the heating gases, a top on said furnace body, an extension on the top of said crucible extending upwardly through said furnace top, said top comprising a detachable annular member of hollow section with a preheater passage extending therethrough, means for conducting to and from said preheater furnace air for use in the furnace, air inlet and outlet branches communicating with said passage, a detachable sealed connection in each of said branches, an annular member of refractory material between the top of the furnace body and the exterior of the crucible and means for cutting off automatically the air and fuel supplies when the furnace is tilted.

11. A tilting furnace including a supporting structure, a furnace body, means for tilting said furnace body on said structure, a crucible mounted in said furnace body and spaced from the Walls thereof by a heating chamber for the circulation of the heating gases, a top on said furnace body, an extension on the top of said crucible extending upwardly through said furnace top, a sealed joint between said crucible and said extension, said heating chamber being closed at a level below that of the top of the crucible so that the heating chamber is entirely separated from the interior of the crucible, an exhaust branch leading from said heating chamber at a level below that at which said chamber is closed, said top comprising a detachable annular member of hollow section with a preheater passage extending therethrough, means for conducting to and from said preheater furnace air for use in the furnace, air inlet and outlet branches communicating with said passage, a detachable sealed connection in each of said branches, and an annular member of refractory material between the top of the furnace body and the exterior of the crucible.

12. A lip-axis tilting furnace including a supporting structure, a furnace body, means for tilting said furnace body on said structure, a crucible mounted in said furnace body and spaced from the walls thereof by a heating chamber for the circulation of the heating gases, a top on said furnace body, means for closing the top of said heating chamber at a level below that of the top of the crucible so that the heating chamber is entirely separated from the interior of the crucible, an exhaust branch leading from said heating chamber at a level below that at which said chamber is closed, said top comprising a detachable annular member of hollow section with a preheater passage extending therethrough, means for conducting to and from said preheater furnace air for use in the furnace, air inlet and outlet branches communicating with said passage, a detachable sealed connection in each of said branches, an annular member of refractory material between the top of the furnace body and the exterior of the crucible and a pouring spout extending through the wall of said furnace body from said crucible.

13. A central axis tilting furnace including a supporting structure, a furnace body, means for tilting said furnace body on said structure, a crucible mounted in said furnace body and spaced from the walls thereof by a heating chamber for the circulation of the heating gases, a top on said furnace body, means for closing the top of said heating chamber at a level below that of the top of the crucible so that the heating chamber is entirely separated from the interior of the crucible, an exhaust branch leading from said heating chamber at a level below that at which said chamber is closed, said top comprising a detachable annular member of hollow section with a preheater passage extending therethrou-gh, means for conducting to and from said preheater furnace air for use in the furnace, said preheater passage extending in said furnace top around the top of the crucible and an annular member of refractory material between the top of the furnace body and the exterior of the crucible.

14. A lip-axis tilting furnace including a supporting structure, a furnace body, means for tilting said furnace body on said structure, a crucible mounted in said furnace body and spaced from the walls thereof by a heating chamber for the circulation of the heating gases, a top on said furnace body, means for closing the top of said heating chamber at a level below that of the top of the crucible so that the heating chamber is entirely separated from the interior of the crucible, an exhaust branch leading from said heating chamber at a level below that at which said chamber is closed, said top comprising a detachable annular member of hollow section with a preheater passage extending therethrough, means for conducting to and from said preheater furnace air for use in the furnace, said preheater passage extending in said furnace top around the top of the crucible, air inlet and outlet branches communicating with said passage, a detachable sealed connection in each of said branches, a pouring spout extending through the wall of said furnace body from said crucible, an annular member of refractory material between the top of the furnace body and the exterior of the crucible, and means for cutting off automatically the air and fuel supplies when the furnace is tilted.

ISAIAH HALL. 

